The invention concerns strand-shaped material, for instance a tubular metallic structure with helical or annular corrugations or an electric cable or an electric line having an armoring which consists of a plurality of wires resting on the surface of the material, which are applied with a long length of lay and are held by a further armoring layer.
Corrugated tubes have the advantage of being both flexible and transversely rigid. Their disadvantage is that when subjected to load by internal pressure they, lengthen in longitudinal direction at first elastically and then plastically, even under slight pressures. It is known to eliminate this disadvantage by placing a braiding around the corrugated tube. The braiding restrains the longitudinal lengthening and, as a result, makes the tubes somewhat more resistant to pressure. Braiding machines are, however, very slow and are extremely expensive, particularly for tubes of large diameter.
From British Patent No. 1 336 630 a corrugated tube is known which is reinforced by a plurality of armoring wires applied with a long length of lay. Over the first armoring layer there is a second armoring layer, also applied with a long length of lay and advantageously applied in the direction opposite to the direction of lay of the first armoring layer. The advantage of this known construction is that as a result of the armoring layers the corrugated tube can take up substantially higher pressures than previously without lengthening as a result of the internal pressure. The disadvantage of the known conduit is that the method of applying the armoring wires is very expensive, particularly when tubes of large diameter are to be armored. Upon the manufacture of such tube it is necessary that the reels which hold the individual armoring wires travel around the longitudinal axis of the traveling corrugated tube.
From Federal Republic of Germany OS No. 27 05 743 it is known to apply a layer of wires onto the surface of an electric cable. Such layers of wires serve, in the cable art, as concentric ground or neutral line. Upon the production of such layers, the layer of wire is held, after application onto the surface of the cable, by a strap which may consist, for instance, of plastic or else of metal.
One important advantage of such a cable provided with a ground or neutral line is that upon the production of a junction point merely the conductor and the insulation need be cut while the ground or neutral conductor can be easily removed from the surface of the cable and remains uncut. Such a technique is known, for instance, from Federal Republic of Germany Utility Model GM No. 18 75 570. It is therefore absolutely necessary that the layer of wire be movable in axial direction. To this extent the known layer of wire cannot be considered an armoring layer which is intended to take up tensile forces.
The object of the present invention is to provide a strand-shaped material which can take up high tensile forces and can be manufactured economically, particularly also in large diameters.